Components manufactured with materials that are chemically unstable in the atmosphere must be protected against contact with the atmosphere.
A typical example for semiconductor components that must be protected against contact with the atmosphere are organic light-emitting diodes (OLEDs), which are generally manufactured with materials that are not resistant to environmental conditions. Other examples are superconductive components based on YBCO (“YBCO” stands for yttrium barium copper oxide, which is a superconductive material) thin films (L. Mex et al. in Applied Superconductivity, 1997. Proceedings of EUCAS 1997 Third European Conference on Applied Superconductivity volume 1, pages 161-164) or electronic components on an organic basis, such as organic field effect transistors (OFET).
Incompatibility with the atmosphere places particular demands on the thickness of encapsulation. In addition, materials that are unstable in the atmosphere are often characterized by high reactivity to many other materials. This means that chemical compatibility between the materials used for encapsulation and the component to be protected must be ensured. Moreover, the thermal resistance of the functional organic materials used in OLEDs is limited. Consequently, another requirement for the encapsulation process is that it must be performed at the lowest possible temperatures. This is especially the case with OLEDs, which are generally only resistant up to temperatures of approx. 100° C.
Another important requirement, in addition to thermal compatibility during the production process, is resistance to thermal stress during the use of the display. Consequently, materials of particular interest for encapsulation are those that exhibit a suitable thermal conductivity for heat removal, thereby protecting the device against overheating.
Another requirement for encapsulation is added when OLEDs are to be applied to flexible substrates, such as polymer foils or chip cards. In this case, the encapsulation must also be flexible.